Schizophrenia is a chronic, disabling, and strongly heritable illness. Postmortem studies suggest reduced cortical dendritic spine density among schizophrenia patients, consistent with structural neuroimaging studies. Likewise, genomic data links schizophrenia-associated common risk variants of greatest effect to disrupted pruning in a rodent model. These convergent lines of evidence suggest that microglia-mediated pruning abnormalities may be responsible for the observed neuropathology in schizophrenia, extending the recognized importance of selective engulfment of synapses by microglia as a means of pruning in normal neurodevelopment. However, large-scale functional studies of human microglia in disease are hampered by difficulties in obtaining living cells from individuals with schizophrenia amenable to rapid screening and quantitative functional assessments. The investigators have recently developed and validated patient-specific models of microglia-mediated pruning by reprogramming induced microglial cells from patient blood isolated monocytes, and assaying them with isolated synapses (synaptosomes) derived from neural cultures differentiated from induced pluripotent stem cells (iPSCs). In preliminary studies, they have demonstrated robust evidence of abnormalities in both microglia as well as synaptosomes from individuals with schizophrenia, and rescued such abnormalities in a dose-responsive fashion with a small molecule probe. The proposed investigation will confirm and extend these results using a very large patient-derived cellular biobank developed by the investigators. Specifically, this study will generate new and fully characterized induced microglia cultures and iPSC-derived neural cultures from 50 individuals with schizophrenia and 50 age, sex, and ancestry-matched healthy controls. These patient-derived reagents will be utilized in an assay to examine functional differences in microglia-mediated synaptic pruning from patients and controls (Aim 1). These assays will also be applied to screen small molecules to identify additional modulators of synaptic pruning, building on promising preliminary data (Aim 2). In parallel, high throughput chemical genomic methods will be applied to characterize transcriptomic effects of these small molecule perturbagens on microglia, providing insight into mechanism of action and facilitating further chemical screens (Aim 3). Together, these studies will further validate the platform for future high-throughput screening efforts aimed at novel therapeutics. The project brings together a team with expertise in cellular modeling, transcriptomics, clinical phenotyping, and small molecule screening. Beyond investigating these principal hypotheses, the project will create a critical resource for the neurobiological community, with high- dimensionality data extending a fully annotated and shareable biobank of patient and healthy control cells.